Mechanical performance of muscular systems is determined by the integration of intrinsic muscle properties, tendon properties, and skeletal mechanics. Performance will be maximized only if these elements operate as a well-integrated or "tuned" system. Jumping performance in frogs presents an ideal model to study musculoskeletal function because both muscle power and tendon energy storage contribute to very large power outputs. The objective is to determine how muscle, tendon, and skeletal elements work together to maximize power output throughout growth. Muscle contractile properties, mechanical advantage and tendon stiffness will be compared at several stages of growth in Bullfrogs and Cuban tree frogs. Total power output will be calculated from jump distance. Muscle mechanical advantage will be measured with force plate and video techniques. Tendon and muscle properties will be measured in vitro with a muscle lever. While properties of tendon, bone and muscle during growth have been studied individually, there is very little understanding of the coordination of the development of these elements. This research will help develop general principles of musculoskeletal design useful to treatment and prevention of injury ,and disease. Information on the development of musculoskeletal structures may be applicable particularly for understanding sport-related injury in children.